Recently, according to an entry system of a vehicle, there has been proposed a device provided in a vehicle which performs an automatic operation by establishing bidirectional communication between a portable machine carried by a vehicle user and a body machine mounted on the vehicle, and then confirming necessary cross-check, which is partially put to practical use.
According to the bidirectional communications since an answer signal including a necessary code is automatically transmitted from the portable machine to the body machine in response to a request signal (a seizing signal activating the portable machine, for example) transmitted from the body machine, a predetermined operation on the vehicle can be performed without any manipulation by the user. For example, according to the entry system of the vehicle, the bidirectional communication is established only when the user having the portable machine comes close to a door of the specific vehicle mounting the corresponding body machine, an unlocking command is automatically output to a locking device of the door in a locked state, and the vehicle door can be automatically unlocked. In addition, such more convenient entry system in which the unlocking or the locking operation of the vehicle door is implemented without requiring intentional manipulation of the user basically is called a passive entry system (or a smart entry system) or the like as a developed type of a general keyless entry, which is needed in market as the one enhancing a product value of the vehicle.
Meanwhile, when this passive entry system transmits a request signal from the body machine only when it is required in order to save a battery power of the vehicle, it is necessary to provide a detection device which detects that the vehicle user approaches or touches the vehicle (a door handle part, for example).
However, as such detection device, an optical or an electrostatic capacity type of sensor or a mechanical switch (so-called microswitch and the like) has been used conventionally. This optical sensor detects that the hand of the vehicle user approaches the door handle, for example, based on an output change of a light-emitting element caused when a light output from the light-emitting element is interrupted by the hand, or an output change of the light-emitting element caused when the light reflected by the hand of the vehicle user is input to the light-receiving element. Meanwhile, the electrostatic capacity type of sensor is a so-called touch sensor which detects the hand when the vehicle user touches the door handle, for example, based on a change in capacity in the sensor because of the touch of the hand, as disclosed in Japanese Unexamined Patent Publication No. 2002-295064.
In addition, as a noncontact type of close-range sensor, as disclosed in International Publication Wo 00/023762, an impulse radar which is used in landmine detection is known.
However, the above-described detection device has the following problems.    (a) In the case of the optical sensor, malfunction could occur because of a stain or a foreign object (rain or a dead leaf, for example).    (b) Since a detection area is small (a detection distance is short), it is difficult to obtain sufficient response so that a problem could occur in the operation of the applied system. For example, in a case the sensor is provided at a handle of a vehicle door in order to trigger request signal transmission in the passive entry system of the vehicle, since the hand of the user is not detected until it approaches and almost touches the sensor (that is, the request signal is not output yet), even when the user pulls up the door handle to open the door, the door is not opened because the automatic unlocking operation is not implemented yet (that is, even when the user tries to open the door in the locked state using the passive entry system, the user cannot open the door because the automatic unlocking operation is not implemented yet and the user feels stuck on the handle) in some cases. Especially, in the case of the electrostatic capacity type of sensor or the mechanical type of switch, the hand of the user is not detected until the hand completely touches the sensor. Thus, in the constitution in which at least the sensor is simply attached to the door handle, since the communication with the portable machine is established after the user starts to pull the door handle to open the door and then the automatic unlocking operation is performed the above problem surely occurs.    (c) Since it is necessary to provide a sensor element which is relatively large and hard to be incorporated, at a place (the door handle of the vehicle, for example) in which the approaching object is to be detected, it is necessary to considerably change a configuration or a size of the place in which the approaching object is to be detected. As a result, the degree of freedom in design at the place is largely limited. Especially, when the hand of the user approaching the door handle of the vehicle is to be detected by the optical sensor or the mechanical type of switch with high response as much as possible, it is necessary to arrange a light-emitting element or a light-receiving element in the vicinity of the door handle or to arrange a contact of the mechanical type of switch at a place projecting from the. door handle, which considerably affects a deign of the door handle or the car body in the vicinity of it.
In addition, as the noncontact type of close-range sensor in which a detection area can be largely set and there is no influence of stains and the like, as described above, the impulse radar which is used in the landmine detector is known. The inventors thought about applying the impulse radar to the above-described sensor. However, since the conventional impulse radar performs complicated judging processes (many waveforms of the reflection waves are sampled, compared and analyzed to determine the existence of the specific object) using a microcomputer, its power consumption is high. Consequently, it was found that it could not be applied to the object sensor of the vehicle using a battery as a power supply. Especially, in the case of the detection device in the above passive entry system of the vehicle, it is necessary to repeatedly and continuously (periodically, for example) carry out a detecting operation in which a detection wave of the radar is output and its reflection wave is received even while the vehicle is stopped so that the hand can be detected whenever it approaches the door handle. Consequently, the power consumption for the detecting operation has to be lowered as much as possible, otherwise the battery of the vehicle runs out soon, that is, the power has to be saved several orders of magnitude more than the landmine detector. As a result, the conventional impulse radar cannot be applied as it is.
It is an object of the present invention to solve the above problems and to provide an object sensor excellent in operation reliability and response, further excellent in mountability (dominance such as in size and design) on a vehicle, and much less in power consumption than conventional impulse radar, using technique of the impulse radar, and a controller using the above sensor.